There are numerous vehicles in use today which have battery-powered electric motors to drive the wheels of the vehicle. These include bicycles, adult tricycles, wheel chairs, motor scooters, golf carts, all terrain vehicles, etc. In many such vehicles, the motor is mounted to the vehicle frame with the motor output being coupled to the wheels by way of a chain drive, gear train or the like.
There also exist in the prior art various bicycles which have an electric motor connected directly to a wheel hub and arranged to rotate that hub. In some cases, the motor is mounted outside the wheel hub and takes up considerable space; see e.g., U.S. Pat. No. 5,622,187. These are not modular assemblies. In other instances, the motor takes the place of the usual wheel hub and rotates the rim of wheel; see, e.g., U.S. Pat. Nos. 552,271; 5,272,938; 5,341,892 and 5,581,136. Such motors are also relatively large, occupying a large percentage of the area within the associated wheel rim.
There do exist a few examples of bicycle-type vehicles whose motor is located entirely within the hub of the wheel; see e.g., U.S. Pat. Nos. 572,036; 2,514,460 and 3,921,741. As to these, in some cases the hub assembly is overly wide so that it cannot be mounted to the fork of a conventional bicycle frame. In other cases, the assembly is composed of a multiplicity of separate parts which are difficult to make and do not assemble as one unit. However, the most serious disadvantage of prior motorized hub assemblies of this general type is that they tend to overheat when used for a prolonged period as the bicycle's or other vehicle's sole source of power. In other words, while those prior assemblies may operate satisfactorily as a power assist device, when used alone to drive the vehicle, they either consume too much power and drain the associated battery after only a relatively short time or they do not develop sufficient torque to enable the vehicle to travel at a sufficient speed particularly on upgrades.